Vascular Endothelial Growth Factor Activates PI3K/Akt/Forkhead Signaling in Endothelial Cells

Abstract

Objective-Vascular endothelial growth factor (VEGF) is a potent angiogenic growth factor that promotes endothelial cell (EC) survival, migration, and permeability. The forkhead transcription factors FKHR, FKHRL1, and AFX are mammalian orthologues of DAF-16, a forkhead protein that controls longevity in Caenorhabditis elegans. In this study, we examined whether VEGF is coupled to phosphatidyl inositol 3-kinase (PI3K)/Akt/forkhead in ECs. Methods and Results-We demonstrate that human ECs express members of the forkhead family (FKHR, FKHRL1, and AFX) and that VEGF modulates the phosphorylation, subcellular localization, and transcriptional activity of one or more of these isoforms by a PI3K/Akt signaling pathway. VEGF inhibited EC apoptosis, promoted DNA synthesis and the G 1 -to-S transition, and reduced expression of the cyclin-dependent kinase inhibitor p27 kip1 . Each of these effects was blocked by the PI3K inhibitor LY294002 or by a phosphorylation-resistant mutant of FKHRL1, but not by wild-type FKHRL1. Conclusions-These

Downregulation of Bim by brain-derived neurotrophic factor activation of TrkB protects neuroblastoma cells from paclitaxel but not etoposide or cisplatin-induced cell death

“…38 It is predominantly regulated by FKHRL1, 21,[23][24][25][26] and the molecular mechanism associated with FKHRL1 regulation has largely been characterized in response to growth factor signaling via the evolutionarily conserved PI3K/Akt survival signaling pathway. [16][17][18][19]39 Using pharmacological inhibitors we found that FKHRL1 was regulated by the PI3K pathway. This is consistent with what has been reported for BDNF activation of endogenous TrkB receptors in SY5Y NB cells by Zhu et al 40 Moreover, a PI3K inhibitor did not block the BDNFinduced reduction of Bim.…”

“…10 Activated Akt phosphorylates and inhibits several proapoptotic proteins, such as Bad, caspase-9 and the Forkhead transcription factors that include FKHRL1, FKHR and AFX, leading to cell survival. [11][12][13][14][15] Although several growth factors (such as IGF-I, TGF, EPO, PDGF) [16][17][18][19] have been found to induce FKHRL1 phosphorylation via the Akt pathway, the role of Akt in BDNF regulation of FKHRL1 has not been explored. Forkhead transcription factor-induced cell death appears to be mediated by transcriptional regulation of a number of genes including Fas ligand (Fasl) 15,20 and Bim, a BH3 only domain protein that modulates the intrinsic mitochondrial death pathway.…”

Phosphatidylinositol 3-kinase/Akt regulates the balance between plasminogen activator inhibitor-1 and urokinase to promote migration of SKOV-3 ovarian cancer cells

“…Given the established link between IGF-1 and insulin with the PI3K/Akt pathway in many cell systems [23,31], we next examined the influence of these growth factors on uPA and PAI-1 levels and their ability to modulate SKOV-3 cell migration. Urokinase expression in SKOV-3 cells was increased by insulin and IGF-1 with a concomitant decrease in PAI-1 (Fig.…”

Pro-apoptotic BIM is an essential initiator of physiological endothelial cell death independent of regulation by FOXO3

“…33 FOXO1 and 4 are expressed in endothelial cells, where they are targets for repression by PI3K/Akt signaling. [26][27][28] Semi-quantitative RT-PCR performed on FACS-sorted, P5 hyaloid endothelial cells showed that Foxo1, and to a lesser extent Foxo4, were more abundantly expressed in hyaloid endothelium than Foxo3 (Figure 4c). To establish whether BIM-dependent hyaloid regression was due to the redundant activity of FOXO transcription factors, we assessed hyaloid vessel regression in mice in which the four FOXO-binding sites located between positions À 625 -þ 2509 of the Bim transcriptional start site had been mutated (Bim DFoxo ).…”

“…[22][23][24][25] FOXO3 is expressed in endothelial cells and is repressed by PI3K/Akt signaling, including in response to VEGF-A in vitro. 26,27 While endothelial cells express multiple FOXO family members, [26][27][28] in vitro studies implicate FOXO3 as the predominant regulator of Bim in this cell type: knockdown of Foxo3 but not Foxo1 resulted in reduced Bim expression in endothelial cells, 27 whereas overexpression of constitutively active FOXO3 induced Bim expression. 29 The requirement for FOXO3 in endothelial cell death in a physiologically relevant context, however, remains to be proven.…”